Influence of over-fired air location on gas-particle flow characteristics within a coal-fired industrial boiler under radial air staging

To achieve low-NOx emission in the coal-fired industrial boiler, the radial air staging method is proposed. The location of the over-fired air (OFA) is an essential parameter as it affects the combustion stability, NOx generation, burnout, and slagging trend. These are related to the gas-particle flow such as the recirculation region, gas mixture, and gas-particle mixture. Therefore, in this paper, taking a coal-fired industrial boiler with radial air staging method as an object, in a cold-modeling furnace, the gas-particle flow characteristics under various OFA locations (LD of 1.29, 1.43, 1.72, and 2.00) are studied. When OFA is radially arranged, the OFA jet diffuses towards the furnace center. As the LD increases, the size of the central recirculation region increases, thereby improving combustion stability. When the LD is 2.00, the mixing of the OFA jet and PCC jet obviously is delayed. Moreover, an increase in LD leads to more returned particles in the furnace center, promoting the reduction reaction of NOx. In addition, as the LD increases from 1.29 to 1.72, the gas-particle mixing uniformity is enhanced, which is beneficial to the uniform temperature distribution. Comprehensively, the LD of 1.43–1.72 is recommended when radial air staging is adopted in coal-fired industrial boilers. •The radial air staging method accelerates the mixing of OFA and the main airflow while reducing the mixing intensity.•With the increase of LD, the obstructing effect by radial OFA on the diffusion of the swirling main airflow is weakened.•The increased LD facilitates gas recirculation in the main combustion zone, which is conducive to stable combustion.•The mixing uniformity of GPF increases with LD in general, promoting the uniformity of temperature distribution.